1. Field of the Invention
The present invention relates to a printing-medium transport apparatus and method for transporting a printing medium by use of two rollers to be driven independently, and to a printing apparatus having such a transport apparatus. The invention is suited particularly for use on an apparatus that handles a highly rigid printing medium.
2. Description of the Related Art
In the printing apparatus as represented by the inkjet printer, a feed mechanism is provided to separate one by one a paper sheet as printing medium, from the holder tray and then transport it by a feed roller toward a transport roller. The transport roller is provided in the printing zone where an image is to be printed. In such a feed mechanism, it is a general practice to place the feed and transport rollers under drive control of separate motor drive systems for the purpose of adjusting the sheet feeding conditions and simplifying the drive mechanism.
Such a feed mechanism must be properly set with timing of drive start and stop in consideration of the load burdened on the sheet being transported by the cooperation of the feed and transport rollers.
For example, Japanese Patent Laid-Open No. 2005-67805 discloses a structure that clutches are provided in the respective drive systems for the feed and transport rollers so that the clutch and drive motor, in each drive system, can be controlled associatively. Meanwhile, Japanese Patent Laid-Open No. H1-271335 describes a structure that tension detecting means is provided to detect a tension in a sheet lying between the feed and transport rollers so that the feed and transport rollers can be placed under drive control associatively depending upon the tension in the sheet detected by the tension detecting means.
However, the provision, of such an especial mechanism as a clutch or such an especial detector as tension detecting means as in the existing art, possibly incurs the complication, size increase and price increase of the transport mechanism and ultimately of the resulting printing apparatus.